Low Coolant Light Comes back every month or two

What is your question?

I was having an issue at about 100k miles where the Low Coolant Light would pop on. I would add coolant and about a month or two later it would come back...same problem. A mechanic(my brother) told me to go to GM dealer and buy some Radiator pellets. They were <$10. Used as directed and now haven't had any issues with loosing coolant in over a year.